1. Field of the Invention
This invention relates to electronic systems, and more particularly to memory management systems and methods.
2. Description of the Related Art
Electronic devices which capture, create, store, manipulate and/or transfer digital music, sound, images, movies or other encoded data have become more prevalent with the advent of less-expensive semiconductor processing and increased consumer demand. Applications such as portable MP3 (Moving Picture Experts Group layer 3 standard) players, PDAs (electronic personal data assistants), digital cameras and digital voice recorders continue to gain popularity. The general trend for each of these electronic applications is to provide greater data storage capability at reduced cost.
Unfortunately, greater memory in these applications is accompanied by an increase in search time when a user attempts to locate a particular file. MP3 players may store hundreds of songs from potentially many different genres. Digital cameras may store hundreds of pictures capturing varied subject matter. Organizing and searching for a particular file is a time-consuming process.
Various types of hashing are used to organize and search for data. Open-address hashing can be used when each record has a single key for organizing. In this method, a hash function f(K) transforms the key into an index location in a hash table in which the record is to be saved. Kyle Loudon, Mastering Algorithms with C 141–142 (O'Reilly & Associates 1st ed.) (August 1999). The record may be found subsequently by re-entering the key into the hash function to find the record's index location. Extendible hashing, another form of hashing, uses the key to determine the portion of memory in which a filed is to be saved. In one example, a hash function is used in combination with a page table having pointers to disk pages. A disk page is a fixed-size portion of memory that may contain many database files. To determine which disk page to use for the file, the record's key is hashed and the most significant bit of the result is used to locate an index location in the page table. The index location points to a disk page where the file is then saved. (See Hashing: from good to perfect, Ron Burk, C Users Journal, 1992, p. 1). To search for the file later, the key is re-entered into the hash function to narrow the search to the particular disk page where the file was saved. Both of these hash methods, while useful for records and files having a single key, are not useful to organize data based on more than one key.
Microsoft® Windows® and Windows CE software, both offered by Microsoft Corporation, organize files by using user-selected alphanumeric names and nested folders which contain the files. A file may be located by searching for its name, or by doing a text search of each individual file. File types, such as word processing documents or executables, may also be used in combination with a file name and folder to help a user find a file. This process is less than optimal when large numbers of files must be searched for files having a particular characteristic or content.
Searching for files is sometimes aided by metadata in the files themselves. Metadata, as used herein, is a key word or words in a metadata field that is attached to the file in a header portion (“interface”) and describes the file's contents. For example, MP3 files include metadata fields that are appended to the audio data. Some MP3 players include programming to enable browsing of MP3 file metadata that identifies track, album, artist, and/or genre as the file is played. See Melissa J. Perenson, CD and MP3: A Match Made in Music Heaven, PC World, April 2001 v19 i4, at 70. Other metadata fields are available that include metadata to identify composer, copyright owner, album/movie/show title, reverb content, equalization content, language, and beats per minute. Martin Nilsson, ID3 Tag Version 2.3.0, p. 1 (Feb. 3, 1999). Canto Software, Inc., offers a Cumulus MP3 Filter product for use on Windows® software to automatically catalog metadata from MP3 file types for later searching. Press Release, Canto Releases Free Cumulus MP3 Filter, Jan. 10, 2001, at 1. The catalog can be searched for title, artist, album, and year for MP3 file searching. Unfortunately, such cataloging greatly increases the amount of data stored in memory because the metadata is reproduced in the catalog.